Induction motor and generator.



R. D; MERsHoN. INDUCTION MOTOR AND GENERATOR.

APPLIOATION FILED APB.. 29, 19.05.`

Patented Feb.. 2, 1909.

3 SHEETS-SHEET 1.

R. E. MBRSHON. INDUCTION MOTOR AND GENERATOR.

APPLICATION FILED APR. 29, 1905.

Patented Feb. 2, 1909.

3 SHEETS-SHEET 2.-

@XH/Wensen R. D. MERSHON. INDUCTION MOTOR AND GENERATOR.

APPLICATION FILED APR. 29,1905.

Patented Feb. 2, 1909.

3 SHEETS-SHEET 3.

w, if; RTM. .mf w., f M uo Mm RALPH D. MERSHON, OF NEW YORK, -N. Y.

INDUCTION MOTOR AND GENERATOR.

Speccation of Letters Patent.

Patented Feb. 2, 1909.

Application inea April 29, i905. serial No. 257,991.

To all whom it may concern:

Be it known that I, RALPH D. MERsHoN, a citizen of the United States,residing at New York, in the county and State of New York, have inventedcertain new and useful Improvements in Induction Motors and Generators,of which the following is a speciiication, reference being had to thedrawing accompanying and forming a part of the same.

My invention relates to alternating current machines of the inductivetype, both motors and generators, and has forits chief object to improvethe operation of such machines. In view of the well known reversibilityof the induction motor,l in that when driven above synchronism it willact as a generator and deliver power to the circuit to which it may beconnected,l the following de'- scription will, for the sake of brevityand simplicity, be confined to the motor; but it vwill be recognized bythose skilled in the art that the invention is. applicable to generatorsas well.

In the induction motor, as in a trans-- former, there is always a.certain amount of stray magnetic field, around the primary and aroundthe secondary windings,-that is to say, a certain amount of magneticllux which is not common to both windings.

erting full torque under normal running conditions. One method ofovercoming this defect is to employ in the secondary, at starting, aresistance, which is usually cut out by.

means of switches, automatically or otherwise actuated, as the motorcomes up tol speed. Switching devices, however, are objectionable'forvarious reasons, and in order to avoid their use, there is sometimesemploy'ed in the secondary a permanently connected resistance, whosevalue is a compromise between that which would be best for ut acompromise resistance is objectionable i since it gives neither the beststarting nor the best running conditions.

Another plan for improving the operation of the motor at starting is touse a condenser in the secondary, and this plan is quite advantageousfrom a number of stand oints. In the rst place, the current taken y thecondenser may be made to neutralize, or even overbalance entirely, thelagging current which the moto;` would otherwise take in starting,Furthermore', by means of the condenser the motor may be made to produceat starting, for a given impressed voltage, a torque greater even thanwith the use of the vbest starting resistance in the secondary. But evenwith a condenser it is in general desirable to have a resistance inshunt with it, through which the current representing the powercomponent in the secondary could flow, althoughv of course suchresistance is not absolutely necessary.

In connection with the'condenser' inthe secondary, switching devices maybe employed for manipulating any resistance which may be used, and, ifso desired, for manipulating the condenser also; but it isl verydesirable to avoid the use of switching devices, and I have tllereforedevised a plan for accom lishin approximately the same result as wou dbe o tained bythe use of'switchin devices automatically or manuallyoperate for cutting out resistance, by means not involvii'ig anyswitching devices in the secondary circuit or circuits, and at the sametime avoiding heavy lagging current at starting. This is the chieffeature of my invention, and it may be stated broadly to consist inconnecting impedance with the condenser, the

two being connected preferably in multiple, l

in the secondary.

As before stated, the object of the condenser is to oifset partially,wholly, or even overbalance, the lagging current taken .by the motor atstarting; and in thelatter case to greatly increase the torque whichcould otherwise be obtained by resistances in the secondary, whetherthey be such as are cut out as thespeed increases, or compromiseresistances. l

The effect of the condenser is maximum when starting, because then thevoltage and frequency across its terminals are greatest but as themotorv increases in lspeed the voltage and frequency across thecondenser teramount.

minals decrease, and the eect of the condenser diminishes. lf atstarting there be connected in shunt with the condenser an impedance orchoking coil, it is possible to so adjust their relative values that thecurrents taken by them will be equal; and since their difference inlcurrent-phase is practically 180 the uadrature components in thev twodevices be neutralized and the current supplied to the combination ofcondenser and impedance will be practically in stepwith theelectromotive force impressed upon them. The condenser may, if desired,be so adjusted that its current will be either greater or less than thatof the impedance, in whichcase the resultant current to the combinationwill be respectively leading or laggin and in the former case, as beforeexplainergl, there will result an increase of tor ue.

or the urpose of explanation let it be supposed t at the currents havebeen made su stantially equal, so that at starting the current to thecombination is practically in step with the impressed electromotiveforce. As the speed ofthe motor increases the current in the lcondenserdecreases rapidly, while that in the impedance lfalls off but slightly,the amount of itsdecrease being dependent upon the ratio of theresistance to the inductance of the impedance coil. However, theimpedance current is all the time, as the speed rises, comin moreclosely into step with the impressed e ectromotive force. The result isthat the resultant current to the combination will not at any speed begreatly lagging. At synchronism the current in both devices will bejzero, but at speeds slightly below synchronous the current in the`impedance may be high while'that in the con-- denser will be small.However, since the reactance component of voltage in the impedance underthese conditions is very low the current in the im edance will vbevery'nearly in stepwith the e ectromotive force, so that the secondarycurrent lags only a very small The result is that at speeds nearsynchronism the secondary is p.actically short circuited, as is'desiredfor such speeds. At speeds between synchronism and zero the current inthe impedance will have departed considerably from unity power factor,but this "ull be more or less compensated for by the Acondenser thuskeeping the power factor of the current to the combination from fallingtc too-,low a vaiue. At zero speedthe current to the combination will,as stated, be

unity, becauseof the adjustment of values made for that purpose. Whennear synchronism, therefore, and at zero speed also, the current tothecombination will be close to unity; but atfintermediate speeds the.power factor may depart more or less from eline? 1f in addition to the'condenser and mpedance there be connected a properly proportionedresistance in shunt t erewith, the current to the resistance will notonly tend to improve the power factor when near synchronism but willalso greatly improve it at intermediate speeds. At the same time thecurrent to this resistance will be such as to increase the tor ue of themotor at any given sli especia y at zero speed or at ot chronism. nderrunning conditions, therefore, the operationvof the motor embodying myinvention will closely a proximate that of one with a short-circuitesecondary, but at Vstarting it will be free from the common objectionsto motors so constructed, in that er s ee s considerably below synthecurrent taken by the mot'or due to the 'secondary current iiowing willbe, if desired,

practically in step with the electromotive force.

If the impedance be over-compensated for by the condenser, as beforementioned, so that the resultant current to the .combination is leading,the magnetizing current required by the motor from the mains will beless than it would be if such over-com'- pensation were not present; andby carrying this over-compensation far enough it is possible. not onlyto neutralize the magnetizing current entirely, which otherwise would betaken by the motor from the supply circuit, but also, if desired, tocause the motor to take a leadin current from the sup ly. Under such conitions it will be seen tlhat the power factor of the motor may be reaterat intermediate speeds than it woul be if the im edance current were notover-- balance and at speeds near synchronism the beneficial eiect ofthe condenser, though small, will be greater than under the conditionjust mentioned.

The plan thus described will answer with the ordlnary condenser, butinorder that the condenser shall not be objectionably large and costly thesecondary of the motor will have to be wound for high voltages and theuse of anything like a squirrel cage winding will be prohibited. This isnot true, however, with a condenser of the electrolytic l cases wherethe ordinary electrostatic condenser could be employed.

When used in the secondary of an induction motor, however, thischaracteristic of the electrolytic i described, with or without aresistance.

.squirrel cage or bart f e..

condenser lis no longer ob'ectionable, but is rather an advantage in tat it is desirable te obtain in the secondary of an induction motor,under given conditions, as .high a loss as possible. We are not,however,coniined to the use of low voltages 'with such a condenser; since byputting the necessary number of elements in sones a condenser may, ifdesired, be obtained which is operar. tive at a high voltage.

Because of the low voltage required by the electrolytic condenser it maybe used in connection with a squirrel cage winding or bar windingsimilar thereto, 'and when so used it may be either inI parallel with aresistance, or with an impedance. or both, or may be used on a vse aratewinding of its own. Where desirab e there might even be three sets ofwindings on the secondary element,-one foruse in connection with thecondensers, one for the resistances, andA one for the impedances.

If the electrolytic condenser be constructed to have suiiciently highloss the. use of resistance in shunt with the condenser and theimpedance, as,l described, may be. avoided. It is to be understood thatinv any case, whether the electrolytic condenser be used or not, the useof resistance is not absolutely necessary, since we may depend on theresistance loss in the impedance o oil as means for obtaining the lossin the second-.wry necessary for producing torue. Furthermore, if it beso desired, instea of employing the resistance in shunt with thecondenser and impedance it may be put in seriels, though in general withless beneiicial resu ts.

Vfl/ien connected t0 separate windings the condenser, impedance, andresistance will perform their functions in starting, in like manner asdescribed when they are connected to the same winding. But by connectingthem toseveral there will result, in addition to structural advantagesin certain cases, a further advantage in that the voltage impressed uponall thev devices of the, Same. kind will be. largely independent' of thestray fields due to the currents taken by the other devices.

From the foregoing the chief` objects of the invention will be seen tobe as follows:

First, to produce anl induction motor which will ad] ust itself forfavorable starting and running conditions. This I attain by employing acondenser and an impedance, as

. Second, to obtain favorable starting or which shall not involve theuse of high vol: tagesarcemplieated windings. butwhich penna theemployment of 0f the 'rhs object 1; sa

by tha-use of. the.- `ectrelyti condenser.. l

relative to the polethe other The invention is shown diagrammaticallyinthe annexeddrawings, in which- Figure 1 is an end view of a portion ofa squirrel cage secondary element, showing condensers, impedances, andresistances connected in multiple to the same set of windings. Fig. lais a detail view of an arrangement like that of Fig. 1, showingcondensers of the electrolytic type. Fig. 2 shows the condensers,impedances, and resistances connected to separate sets of windings. Fig.3 shows a secondary with two sets of windings, each having its own setof condensers, pedances, and resistances, the two windings eing arrangedto overlap. Fig. 4 shows three overlapping windings, each having its ownset of condensers, impedances, and re-x sistances. Fig. 5 illustrates'the invention 'embodied in a motor adapted to run at differ.l

ent speeds by varying the number of its poles.

Throughout the drawings, the condensers are indicated by c, impedancesby t, and rev sistances by 1', wherever they occur.

-In Fig. 1 (and Fig. la) the condensers, impedances and resistances areall connected to the same set of windings., like devices being in serieswith each other but in multiple with the remaining devices.. In Fig. 2the similar devices are also in series with each other but areconnected` to separate sets of windings. Thus, calling the barindicatedby- A the first,- the condensers are connected thereto and to everythird bar therefrom, and the resistances and impedances to theintermediate bars respectively. The extent of the overlapping may bevaried if desired, by making the different circuits extend over four,five or in general any number of bars, as may be most advantageous,under iven conditions. I'n any case' the voltage e ective acrossthetermiaalaof. the devices will depend, other things being equal, uponthe spacing of they Qwuit-S itc of the primary,` the rule being, 1ngenera upto and including the primary pole-pitch, that the wider thecircuit the greater the voltage be.v Hence the voltage on the devicesconnected asin Fig. 2. will be much greater than. in the arrangementshown in Fig. 1. The proper proportioningof the circuits, as well as,the valuesof; the devices used, mayA be` effected by any one skilled inthe'art to which the invention pertains. Y

In Fig. 3 thel secondary element has two. sets of windings, composed ofalternated bars. Each set of. windings has connected vwith it completesets of oondensers,

dances, and resistaneeS,they like devices bein in series. with eachother and in multi le. wi p Inliigber@ aret sets of.` each. providedwith devices. eenneeted with each other as Fig- 3. The use of overlppmgcircuits-accomplishes the same results as regarda voltage. as befQreex-vdesigns the apparatus.

plaine'd, so that the voltage in Fig. 4 woulde greater than in Fig. 3,and in both greater than in Fig. i.

The values to be given to the various devices Will depend entirely onthe results desired for the performance of the machine, but thenecessary proportioning ofthe same may be readily made by the skilledengineer who applies the invention.

The mechanical details, as regards the manner of arranging the devicesand connecting them with the motor, are immaterial, and are vbest leftto theengineer who The devices may be located and secured in thesecondary element itself, or they may be entirely outside of the same,or part of them outside, as desired, those outside being connected bymeans of slip-rings if the secondary is the moving eiement of themachine. Whichever plan is to be employed will in general be determinedby what is most convenient or otherwise desirable under givenconditions. Y

ln the foregoing explanation nothing has been said with reference to theapplication of the invention to machines adapted for speed-control byvarying the number of its poes, but it is clear that the invention isthus applicable. in fact it is of special value in apparatus of thatcharacter, as aording means for overcoming one, at least, of theprincipal drawbacks met with in machines adapted for such s eed-control,namely, increase of magnetic eakage in such motors as the number ofpoles is increased. Furthermore, in addition to the fact that thegeneral principles before explained are especially advantageous forvariable-pole motors, the use of an electrolytic condenser, enabling asit does the application of these principles to squirrel. cage or barwindings, is of particular imp-ctance in that such windings lendthemselves more readily to the construction of variable-pole motors,since such windings accommodate themselves to any ole-pitch, and do sowith special facility if t e spacing of the bars .be suiciently small,so that the spacing is less than the small pole-pitch to be employed.

Fig. 5 shows a variable-pole motor, adapt-- ed to run' with two and withfour poles, thus ving two synchronous speeds. In this e G indicates thesource of current,

' which may be either single-phase, as shown,

or polyphase. P is the primary 0f the machine, of any' suitable kind, asfor exam le the single ring windingshown. C is a agrammatic controller.By tracing the connections it will be seen that in the iirst position ofthe controller two poles will be pr'o' duced in thev primary, the leadstherefor belng tapped in at 1 and 1 ln the next osition, the-number ofpoles, is changed to consisting of two or more electrodes our, producedby leads 1, 1', l, 1. The

ernia? secondary element, S, shown in Fig. 5 is of the type illustrated.in Fig. that is, with the condensers, resistance; and impedances allconnected to the same winding, but it is clear that any secondaryembcdyin the principle of my invention may be emp oyed 1n the motor andit is therefore unnecessary to repeat Fig. 5 merely to show dierentsecondaries therein. it -(is also evident that the range of pole-numbersshown in Fig. 5,

that is, two and four, is merely'illustrative, 'and that the applicationof the invention is not limited thereto.

As i have already explained, the use of resistance with the vcondenserand impedance, though generally advantageabsolutely essential to theinven pecially where anelectrolyticcondenser employed; and though theresistance is many cases a desirable addition l do net consider myseHlimited thereto so far as ther broad invention vis concerned.

. By the term electroiytic cond wish to be understood to denser of thattype, as opp: dinary so-called electrostatic condem er.. electrolyticcondenser ,may be described broadly, in its commonest form, as beingmersed in an electrolyte, but the concrete forms of the devices may varywiday. y

In certain of the claims i have specified that like devices"7 are inseries' with each other. l do not mean by this that the cnrA rentnecessariiy iiows from to the other.

ln fact the termine-.lsV of the devices were spaced the salme distanceapart as the poi-epitch of he primary there would be at times no currentflowing rrom cneto another. But I mean rather, in the claims referredto, that the end of one device is connected to the beginning of another.:in other claims I have specified that the devices are connected to t esecondary winding or windings points relative. thereto, by, which meanis not that the points of connection do not shift in every revolution ofthe rotor, as would bethe case if the connections were made through acommutator.

Special reference has been made throughout to squirrel cage `or.4harwindings?, and only windin s of this kind are shown 1n the drawings. utit is to be understood that the invention is not limited thereto, but isin Afact applicable to all lother types of windings as Well.

lt will be evident from the forego' ithat by means of my invention it ispossi le to produce amotor Whose erformance will be com arable to oreven etter than-that-o one aving resistance in its secondary which iscut out as the speed increases; and this without the employment ofswitches or actuating de 'ces of any kind, thoughit v lio in addition ifdesired. It is also evident thatin a motor embodying my invention it ispossible to obtain torques considerably greater than could be obtainedunder simiar conditions in a motor having secondary rheostatic control.

Having now described my invention, what I claim is:

1. In an alternating current machine of the induction type, a secondaryelement having a winding or windings, and one or more condensers,resistances, and impedances,

connected with thesecondary winding or windings, as set forth. I

2. In an alternating current machine of the induction type, a secondaryelement having a winding or windings, and one or more impedances andelectrolytic condensers connected with the secondary winding or windingsat fixed points relative thereto, as set forth.

3. In an alternating current machine of the induction type, a secondaryelement having a winding or windings, and one or more impedances,resistances, and electrolytic condensers connected with the secondarywinding or windings, as set forth.

4. In an alternating current machine of the induction type', a secondaryelement having a winding or windings, and one or more electrolyticcondensers connected with the winding or windings at iXed points reative thereto, as set forth.

5. In an alternating current machine of the induction type, a secondaryelement having a winding or windings, and one or more condensers,resistances, and impedances, connected with the secondary winding orwindings, like devicesbeing connected-in series with each other, as setforth.

6. In an alternating current machine of the induction type, a secondaryelement having a winding or windings, and one or more impedances andelectrolytic condensers connected with the secondary winding orwindings, like devices being connected in series with each other, as setforth.v

7. In an alternating Y current machine of the induction type, asecondary element having a winding or windings, and one or moreimpedances, resistances, and electrolytic condensers connected with theIsecondary windings, like devices being connected in series with eachother, as set forth.

8. In an alternating current machine of the induction type, a secondaryelement having a plurality of windings, andy one or more condensers, oneor more impedances, and one .or more resistances, connected withdifferent windings, as set forth. 9. In an alternating current machlneof 'the induction type, a secondary element having a 'plurality ofoverlapping windings` and one or more condensers, one or moreimpedances, and one or more resistances, connected with differentwindings, as set forth.

10. In an alternating'current machine of the induction type, a secondaryelement having a plurality of windings, and a plurality of .independentsets of condensers, impedances,

and .resistances, connected with separar. J windings, as set forth.

11. In an alternating current machineof the induction type, a secondaryelement having a plurality of overlapping windings, and a plurality ofindependent sets of condensers,

ings, as set forth.

13. In an alternating current machine of the induction type, thecombination with the primary element, and means for varying the numberof poles therein, of a secondar element having one or more sets ofsquirre cage windings, and one or more eletrolytic condensers connectedwith the secondary winding or windings, as set forth.

14. In an alternating current machine of the induction type, thecombination with the primary element, and means for varying the numberof poles therein, of a secondary element having one or more sets ofwindings, and one or more impedances, and one or more electrolyticcondensers connected with the l.secondarywinding or windings, as setforth.

15. In an alternating current machine of the induction type, thecombination with the primary element, and means for varying the numberof poles therein, of a secondary element having one or more sets ofsquirrel cage windings, and one or more imnedanccs, and one or moreelectrolytic condensers connected with the secondary winding orwindings, as set forth.

16. In an alternating current machine of the induction type, thecombination with the primary element and means for varying the number of`poles therein, of a secondary element havingy one or more sets ofwindings, and one or morecondensers, im edances, and resistances,connected with t e secondary windin or windings, vas set forth.

17. n an alternating current machine of the induction type, thecombination with the primary element, and means for var Ting the numberof poles therein, of a secon ar element having one or more sets ofsquirre cage windings, and one or more condensers, im-

. impedances, and resistances, connected with ing connected withdifferent' secondary wind-4 ings, as set forth.

i9. in an alternating current machine of the induction' type, thecombination with the primary element, and means for varying the numberof poles therein, of a secondary element having a plurality ofoverlapping squirrel cage windings, the conductors thereof being spacedless distance apart than the polepitch of the rimary with its greatestnumber of goles, an a plurality of sets of im edances an electrolyticcondensers, the sai sets being connected with different secondarywindings, as set forth. i

'20. in an alternating current machine of the induction type, thecombination with the primary element and means for varying the number ofpoles therein, of a secondary element having a plurality of overlappingsquirrel cage windings, the conductors thereof being spaced lessdistance apart than the polepitch of the primary element with thegreatest number of poles, and a plurality of sets of impedances,resistances, and electrolytic condensers, the said sets being connectedwith different secondary windings, as set forth.

21. In an alternating current machine of the induction type, a secondaryelement having a plurality of windings, one having relatively lowinductance, another having relatively high resistance, and capacity inone or more of theplurality of windings, as set forth. 22. in analternating current machine of the induction type, a secondary elementhaving a plurality of windings, one having relatively high inductance,another having relatively high resistance, and a third having relativelyhigh capacity, as set forth.

23. in 'an alternating current machine of the induction type, asecondary element having a plurality of windings, one havingrelativelyhigh inductance and low resistance, another having relativelylow inductance and high resistance, and capacity in one or more of theplurality of windings, as set forth.

24. In an alternating current machine of the induction type, a secondaryelement having va plurality-of windings, one having relatively highinductance and low resistance, another having relatively low inductanceand high resistance, and a third having relatively high capacity, as setforth.

RALPH D.`MERSHON.

Witnesses:

S. S. DUNHAM,

LAWSON DYER.

